searching for Crank

Whichever crank is used, it will need to be rebalanced.

* Early 273 cranks had a small converter register so a more common, later model converter with the larger snout will not fit without machining the back of the crank.

* Some earlier 318's had forged cranks. Forged 318 truck cranks use to be favorites because they were stronger. I believe the journals were solid, but i don't recall for sure. I have one with a worn thrust surface somewhere in my garage.

* "We want to drill a 318 to 340 and therefore we need the 340 crankshaft"
If this means boring out an OEM 318 to a 340 bore, then I would not recommend it. 318 cylinder walls would end up too thin for proper ring seal and overall strength.